104 Задачка по химии №010 404

Which atom or ion performs the function of an oxidizing agent in the above reactions, and which one - the function of a reducing agent:
A) (NH4)2Cr2O7 → N2 Cr2O3 H2O
B) KNO3 → KNO2 O2
C) AgNO3 → AgNO2 O2
D) Pb(NO3)2 → PbO NO2 O2

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